CN116438734A

CN116438734A - Vehicle electrical system

Info

Publication number: CN116438734A
Application number: CN202180071574.6A
Authority: CN
Inventors: S·哈格宾
Original assignee: Zhejiang Geely Holding Group Co Ltd; Ningbo Geely Automobile Research and Development Co Ltd
Current assignee: Zhejiang Geely Holding Group Co Ltd; Ningbo Geely Automobile Research and Development Co Ltd
Priority date: 2020-10-23
Filing date: 2021-09-09
Publication date: 2023-07-14
Also published as: EP3988377A1; US20230226936A1; WO2022083341A1; EP3988377B1

Abstract

A vehicle electrical system comprising: an electrical storage system (6); a first multiphase electric power machine (5 a) having a plurality of stator windings (8) connected to a common neutral point; a first inverter (9 a) operatively connected to the electrical storage system (6) and the first multiphase electrical machine (5 a), wherein the first inverter (9 a) has a plurality of switch leads (10, 11, 12) with switches (10 a, 10b, 11a, 11b, 12a, 12 b); a second multiphase electric power machine (5 b) having a plurality of stator windings (13) connected to a common neutral point; a second inverter (9 b) operatively connected to the electrical storage system (6) and to the second multiphase electrical machine (5 b), wherein the second inverter (9 b) has a plurality of switch leads (14, 15, 16) with switches (14 a, 14 b); a bi-directional buck-boost DC/DC converter operatively connected to a common neutral point of the first multi-phase electric machine (5 a) and a common neutral point of the second multi-phase electric machine (5 b) and configured for using at least one stator winding of each of the first and second multi-phase electric machines (5 a, 5 b) as a buck-boost inductance; a bi-directional AC/DC converter operatively connected to the DC/DC converter and to the charging terminal (7), with or without intermediate electrical filter means; and an electronic control system (21) for controlling the operation of the vehicle electrical system.

Description

Vehicle electrical system

Technical Field

The present disclosure relates to vehicle electrical systems and to methods for charging an electrical storage system of a vehicle electrical system.

The vehicle electrical system and related methods according to the present disclosure may be implemented in a vehicle, such as an electric vehicle or a hybrid vehicle. However, the vehicle electrical system and related methods according to the present disclosure are not limited to this particular vehicle, but may alternatively be installed or implemented in other types of vehicles, such as trucks, buses, rail vehicles, flying vehicles, marine vessels, off-road vehicles, mining vehicles, agricultural vehicles, work vehicles (such as wheel loaders or excavators), forest vehicles (such as harvesters or trucking vehicles), motorcycles, and the like.

Background

In the field of vehicle electrical systems, particularly electrical systems for plug-in electric vehicles, there is a constant need for further improvements in performance, operational life and cost effectiveness.

For example, document US 2010/096926 A1 discloses a traction inverter circuit comprising a first energy storage device configured to output a dc voltage, a first bi-directional dc-to-ac voltage inverter coupled to the first energy storage device, and a first electromechanical device. However, despite some activity in this area, there remains a need for further improvements in vehicle electrical systems, particularly in terms of improved compactness, weight and cost effectiveness.

Disclosure of Invention

It is an object of the present disclosure to provide a vehicle electrical system that avoids the aforementioned problems. This object is at least partly achieved by the features of the independent claims.

According to a first aspect of the present disclosure, there is provided a vehicle electrical system comprising: an electrical storage system; a first multiphase electrical machine having a plurality of stator windings connected to a common neutral point; a first inverter operatively connected to the electrical storage system and the first multi-phase electrical machine, wherein the first inverter has a plurality of switch leads with switches; a second multiphase electrical machine having a plurality of stator windings connected to a common neutral point; a second inverter operatively connected to the electrical storage system and to the second multi-phase electrical machine, wherein the second inverter has a plurality of switch leads with switches; a bi-directional buck-boost (buck-boost) DC/DC converter operatively connected to the common neutral point of the first multi-phase electric machine and the common neutral point of the second multi-phase electric machine and configured for using at least one stator winding of each of the first multi-phase electric machine and the second multi-phase electric machine as a buck-boost inductance; a bi-directional AC/DC converter operatively connected to the DC/DC converter and the charging terminal with or without an intermediate electrical filter device; and an electronic control system for controlling operation of the vehicle electrical system.

According to a second aspect of the present disclosure, a method for charging an electrical storage system of a vehicle electrical system is provided. The method comprises the following steps: connecting a first inverter to the electrical storage system and to a first multiphase electrical machine having a plurality of stator windings connected to a common neutral point, wherein the first inverter has a plurality of switch leads with switches; connecting a second inverter to the electrical storage system and to a second multiphase electrical machine having a plurality of stator windings connected to a common neutral point, wherein the second inverter has a plurality of switch leads with switches; connecting a bi-directional buck-boost DC/DC converter to a common neutral point of the first multi-phase electric machine and a common neutral point of the second multi-phase electric machine to use at least one stator winding of each of the first multi-phase electric machine and the second multi-phase electric machine as a buck-boost inductance; connecting the bi-directional AC/DC converter to the DC/DC converter and the charging terminal with or without an intermediate electrical filter device; and, providing an electronic control system for controlling operation of the vehicle electrical system.

In this way, a vehicle electrical system is provided that is capable of being charged by single-phase or three-phase alternating current having a wide input voltage range, while an internal electrical storage system may also be configured for use with various operating voltage levels. Furthermore, since the DC/DC converter is located outside the electrical power system, electronic power switches can be used that are less powerful and therefore less costly. For example, in contrast to having a DC/DC converter located outside of the power system so that the windings of the electric machine can be used as a buck inductor and a relatively low performance switch, such as a switch having a maximum current capacity rating of only 30 amps, a DC/DC converter located within the power system typically requires not only a large/heavy inductor for buck operation, but also a relatively expensive switch that may have a capacity of approximately 200-400 amps.

Furthermore, by using the windings of the electric machine as buck/boost inductors, the cost and weight of the individual buck/boost inductors may be reduced. Finally, the bi-directional design of the AC/DC converter and the DC/DC converter enables the electrical storage system to be used for vehicle to grid power.

Further advantages are achieved by implementing one or several of the features in the dependent claims.

In some exemplary embodiments, the electronic control system is operably coupled to the first inverter and the second inverter and is configured to control operation of the first inverter and the second inverter for controlling the first multi-phase electric machine and the second multi-phase electric machine, respectively, during an operational mode in which the vehicle electrical storage system is powered.

In some exemplary embodiments, the electronic control system is operably coupled to the bi-directional DC/DC converter and the first and second inverters and is configured to: during a vehicle charging mode of operation, controlling operation of the DC/DC converter and the first and/or second inverter for converting direct current supplied from the AC/DC converter into modified direct current and supplying the modified direct current to the electrical storage system via a common neutral point of the first and second multi-phase electrical machines; and during a vehicle-to-grid mode of operation, controlling operation of the first and/or second inverter and the DC/DC converter for supplying direct current from the electrical storage system to the DC/DC converter via a common neutral point of the first and second multi-phase electrical machines and for converting the direct current into modified direct current for supply to the AC/DC converter. Thus, a wide versatility (versatility) is achieved by the bi-directional nature of the vehicle electrical system as a whole, and in particular of the DC/DC converter.

In some exemplary embodiments, the electronic control system is operably coupled to the bi-directional AC/DC converter and configured to: during a vehicle charging mode of operation, controlling operation of an AC/DC converter for converting single-phase alternating current or multi-phase alternating current received from a vehicle external charging power source via a charging terminal into direct current for supplying the direct current to the DC/DC converter; and during a vehicle-to-grid mode of operation, controlling operation of the AC/DC converter for converting direct current received from the DC/DC converter into single-phase alternating current or multi-phase alternating current for supplying the alternating current to an electrical load external to the vehicle via the charging terminal. Thus, a wide versatility is achieved by the bi-directional nature of the vehicle electrical system as a whole, and in particular of the AC/DC converter.

In some exemplary embodiments, the bi-directional buck/boost DC/DC converter is a non-isolated switching converter having two bi-directional switching devices, and the DC/DC converter relies on the inductance of one or more stator windings of each of the first and second multi-phase electric machines as an energy storage element for achieving voltage buck during the vehicle charging mode and voltage boost during the vehicle-to-grid mode of operation. Thereby, a separate inductor element with a large weight and space requirement can be dispensed with. For example, the inductor coil of a buck/boost DC/DC converter for a 5-10kW charger for an electric vehicle typically has a weight of about 5-7 kg.

In some exemplary embodiments, the AC/DC converter has a grid side with two or three connection points for receiving and outputting single-phase or three-phase alternating current and an electric machine side with a first connection point and a second connection point for receiving and outputting direct current, and the DC/DC converter comprises a first bidirectional switching device configured for selectively opening and closing an electrical connection between the first connection point of the AC/DC converter and a common neutral point of the first multi-phase electric machine and a second bidirectional switching device configured for selectively opening and closing an electrical connection between the common neutral points of the first multi-phase electric machine and the second multi-phase electric machine. Thereby, a relatively more cost-effective DC/DC converter design is achieved.

In some exemplary embodiments, during a vehicle charging mode of operation, the control system is configured to operate the DC/DC converter while voltage down controlling each of the first and second bi-directional switching devices to have alternating on and off periods such that, during a first phase, when the first bi-directional switching device is on and the second bi-directional switching device is off, current can flow from a first connection point of the AC/DC converter, via the first bi-directional switching device, one or more stator windings of the first multi-phase electric machine, the first inverter, the second inverter (via simultaneous bypass or non-bypass at a preceding few to the electric storage system), and via one or more stator windings of the second multi-phase electric machine, and back to a second connection point of the AC/DC converter; and, such that, during the second phase, when the first bi-directional switching device is off and the second bi-directional switching device is on, the charging current is able to pass from the negative pole of the electrical storage system, via the second inverter, the one or more stator windings of the second multi-phase electrical machine, the second bi-directional switching device, the one or more stator windings of the first multi-phase electrical machine, the first inverter, and back to the positive terminal of the electrical storage system. The design provides an easy to implement and cost effective overall design of the vehicle electrical system and has a high degree of versatility in terms of input voltage levels and electrical storage system voltage levels.

In some exemplary embodiments, during the vehicle charging mode of operation, the control system is configured to operate the first bidirectional switching device with a first set of alternating on and off periods and to operate the second bidirectional switching device with a second set of alternating on and off periods that are set to be substantially synchronous and inverted with the first set of alternating on and off periods. Thereby, a direct and relatively easy to implement control strategy of the DC/DC converter is provided.

In some exemplary embodiments, the control system is configured to charge the electrical storage system in a voltage step-down mode using electrical energy supplied from a charging source external to the vehicle via the AC/DC converter by operating the first and second bi-directional switching devices synchronously and with alternating on and off cycles.

In some exemplary embodiments, the control system is configured to charge the electrical storage system in the voltage step-down mode by setting the first bidirectional switching device to a closed state (or vice versa) when the second bidirectional switching device is set to an open state.

In some exemplary embodiments, each of the first inverter and the second inverter comprises at least one inverter leg for each phase of the associated multi-phase electric machine, and each inverter leg comprises an upper switch associated with the positive dc bus, the upper switch being connected in series with a lower switch associated with the negative dc bus, wherein the control system is configured to set all of the upper and lower switches of the first inverter and the second inverter to an open state during both the first phase and the second phase during the vehicle charging mode of operation. This way less electrical losses can be generated, since the switching operation of the inverter switches is eliminated during the charging operation mode.

Alternatively, the control system is configured to set all upper and lower switches of the first inverter and the second inverter to an open state during both the first phase and the second phase, to set all upper and lower switches of the first inverter and all lower switches of the second inverter to an open state during both the first phase and the second phase, to set one, two, three or more upper switches of the second inverter to a closed state during the first phase, and to set all upper switches of the second inverter to an open state during the second phase during the vehicle charging mode of operation. Thus, the inductance of one or more particular stator windings of the second electric machine may be utilized to achieve a desired buck conversion during the charging mode of operation.

Alternatively, the control system is configured to set all upper and lower switches of the first and second inverters to an open state during both the first and second phases, to set all upper and lower switches of the second inverter and the first inverter to an open state during both the first and second phases, to set one, two, three or more lower switches of the first inverter to a closed state during the first phase, and to set all lower switches of the first inverter to an open state during the second phase during the vehicle charging mode of operation. Thus, the inductance of one or more particular stator windings of the first electrical machine may be utilized to achieve a desired buck conversion during the charging mode of operation.

In some exemplary embodiments, wherein the electrical connection extending from the common neutral point of the first multi-phase electrical machine to the common neutral point of the second multi-phase electrical machine via the second bi-directional switching device is devoid of any substantial inductor. Thereby, significant weight reduction can be achieved.

In some exemplary embodiments, the vehicle electrical system is devoid of a DC/DC converter in an electrical power supply path extending between the electrical storage system and any of the first inverter and the second inverter. Thus, a lower cost DC/DC converter may be implemented in view of having a lower current level associated with single-phase or three-phase charging than a relatively expensive and high current level switch disposed within the powertrain.

In some exemplary embodiments, the AC/DC converter is a single-phase or three-phase active front-end rectifier comprising a plurality of switch legs connected between a direct-current link positive bus and a negative bus, wherein each switch leg has at least two switches connected in series via an intermediate conductor, wherein the grid side of the AC/DC converter comprises two or three connection points electrically connected to a charging terminal for receiving single-phase or three-phase alternating current from a vehicle external charging source or outputting single-phase or three-phase alternating current to a vehicle external load, wherein each of the two or three connection points is electrically connected to a separate intermediate conductor of the plurality of switch legs.

In some exemplary embodiments, during a vehicle-to-grid mode of operation, the control system is configured to operate the DC/DC converter while voltage boosting each of the first and second bi-directional switching devices to have alternating on and off periods such that, during the first phase, current can flow from the positive pole of the electrical storage system via the first inverter, one or more stator windings of the first multi-phase electrical machine, the second bi-directional switching device, one or more stator windings of the second multi-phase electrical machine, the second inverter, and back to the negative terminal of the electrical storage system when the first bi-directional switching device is off and the second bi-directional switching device is on; and thereby enabling current to flow from the second connection point of the AC/DC converter, via the one or more stator windings of the second multi-phase electric machine, the second inverter, the electrical storage system, the first inverter, the one or more stator windings of the first multi-phase electric machine, the first bi-directional switching device, and back to the first connection point of the AC/DC converter, when the first bi-directional switching device is on and the second bi-directional switching device is off during the second phase. Thereby, a high versatility of the vehicle electrical system is achieved.

In some exemplary embodiments, each of the first inverter and the second inverter comprises one inverter leg for each phase of the associated multi-phase electric machine, and each inverter leg comprises an upper switch associated with the positive dc bus connected in series with a lower switch associated with the negative dc bus, wherein the control system is configured to set one, two, three or more upper switches of the first inverter to a closed state during both the first phase and the second phase, set one, two, three or more lower switches of the second inverter to a closed state during both the first phase and the second phase, and set all lower switches of the first inverter and all upper switches of the second inverter to an open state during both the first phase and the second phase. Control of the switches of the first inverter and the second inverter may provide various inductance levels as appropriate for various specific situations and implementations.

In some example embodiments, the control system is configured to control the first inverter and/or the second inverter based on an angular position of a rotor of the first multi-phase electric machine and/or the second multi-phase electric machine during a vehicle-to-grid or a vehicle charging mode of operation. Thus, the desired total inductance for buck/boost operation can be better selected as the case may be.

In some example embodiments, the control system is configured to select which of the one or more upper switches of the first inverter and which of the one or more lower switches of the second inverter should be set to a closed state during the first phase and the second phase based on an angular position of a rotor of the first multi-phase electric machine and/or the second multi-phase electric machine during the vehicle-to-grid mode of operation; and/or during a vehicle charging mode of operation, selecting which of the one or more upper switches of the second inverter should be set to a closed state during the first phase or which of the one or more lower switches of the first inverter should be set to a closed state during the first phase based on an angular position of a rotor of the first and/or second multi-phase electric machine. Thus, the desired total inductance for buck/boost operation can be better selected as the case may be.

In some example embodiments, wherein the control system is configured to select which of the one or more upper switches of the first inverter and which of the one or more lower switches of the second inverter should be set to the closed state during the first phase and the second phase based on a maximum current of the switches of the first inverter and/or the second inverter during the vehicle-to-grid mode of operation, and/or to select which of the one or more upper switches of the second inverter should be set to the closed state during the first phase or which of the one or more lower switches of the first inverter should be set to the closed state during the first phase based on a maximum current of the switches of the first inverter and/or the second inverter during the vehicle charging mode of operation. It is clear that in an operational setting involving the routing of said current through a single stator winding, if the charging or discharging current exceeds the maximum rated current value of any switch of the first inverter and/or the second inverter, the charging/discharging current must be divided among a plurality of different switches of said first inverter and/or second inverter in order to reduce the individual load on the respective switch.

In some exemplary embodiments, the method further comprises the steps of: providing a DC/DC converter with a first bidirectional switching device configured for selectively opening and closing an electrical connection between a first connection point of the AC/DC converter and a common neutral point of the first multi-phase electric machine and a second bidirectional switching device configured for selectively opening and closing an electrical connection between the common neutral points of the first and second multi-phase electric machines; and controlling each of the first and second bi-directional switching devices to have alternating on and off periods for achieving voltage step-down during a vehicle charging mode of operation, wherein, during a first phase, when the first bi-directional switching device is on and the second bi-directional switching device is off, current flows from a first connection point of the AC/DC converter, through the first bi-directional switching device, one or more stator windings of the first multi-phase electric machine, the first inverter, the second inverter (via simultaneous bypass or non-bypass at a first few places), and through one or more stator windings of the second multi-phase electric machine, and back to a second connection point of the AC/DC converter, and wherein, during the second phase, when the first bi-directional switching device is off and the second bi-directional switching device is on, charging current flows from a negative pole of the electric storage system back to the positive terminal of the electric storage system via the second inverter, one or more stator windings of the second multi-phase electric machine, the second bi-directional switching device, one or more stator windings of the first multi-phase electric machine, and the first inverter.

In some exemplary embodiments, the method for charging an electrical storage system further comprises the steps of: providing a DC/DC converter with a first bidirectional switching device configured for selectively opening and closing an electrical connection between a first connection point of the AC/DC converter and a common neutral point of the first multi-phase electric machine and a second bidirectional switching device configured for selectively opening and closing an electrical connection between the common neutral points of the first and second multi-phase electric machines; and controlling each of the first and second bi-directional switching devices to have alternating on and off periods for achieving voltage boost during the vehicle-to-grid mode of operation, wherein, during a first phase, current flows from the positive pole of the electrical storage system, via the first inverter, the one or more stator windings of the first multi-phase electrical machine, the second bi-directional switching device, the one or more stator windings of the second multi-phase electrical machine, the second inverter, and back to the negative terminal of the electrical storage system, when the first bi-directional switching device is on and the second bi-directional switching device is off, and wherein, during a second phase, current flows from the second connection point of the AC/DC converter, via the one or more stator windings of the second multi-phase electrical machine, the second inverter, the electrical storage system, the first inverter, the one or more stator windings of the first multi-phase electrical machine, the first bi-directional switching device, and back to the first connection point of the AC/DC converter.

Other features and advantages of the invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present disclosure can be combined to create embodiments other than those explicitly described above and below without departing from the scope of the present disclosure.

Drawings

The present disclosure will be described in detail below with reference to the attached drawing figures, wherein,

figure 1 schematically illustrates a side view of a vehicle including a vehicle electrical system according to the present disclosure,

figure 2 schematically illustrates a layout of a vehicle electrical system according to the present disclosure,

figure 3 shows an exemplary embodiment of a more detailed layout of an electrical system according to the present disclosure,

figure 4 schematically shows an exemplary embodiment of the operation of the first switching means and the second switching means,

figures 5A-5B schematically illustrate a first strategy for controlling a charging current of an electrical system according to the present disclosure,

figures 6A-6B schematically illustrate a second strategy for controlling the charging current of an electrical system according to the present disclosure,

figures 7A-7B schematically illustrate a third strategy for controlling the charging current of an electrical system according to the present disclosure,

Figures 8A-8B schematically illustrate strategies for controlling the discharge current of an electrical system during a vehicle-to-grid mode of operation according to the present disclosure,

fig. 9 schematically shows the layout of fig. 3 with further details, which are relevant for the electrical filter arrangement according to the present disclosure,

figure 10 schematically illustrates a three-phase version of an electrical system according to the present disclosure,

figures 11-13 schematically illustrate basic steps of some methods for providing and operating an electrical system according to the present disclosure,

fig. 14 schematically shows the layout of fig. 10 with further details relating to an electrical filter arrangement according to the present disclosure, an

Fig. 15 schematically shows that a three-phase version of the electrical system can be connected to a single-phase power supply without any hardware modifications.

Detailed Description

Various aspects of the present disclosure will be described below in connection with the accompanying drawings to illustrate and not limit the disclosure, wherein like reference numerals denote like elements, and variations of the described aspects are not limited to the specifically illustrated embodiments, but are applicable to other variations of the disclosure.

The vehicle electrical system according to the present disclosure is configured to be implemented in a hybrid vehicle or an all-electric vehicle (e.g., an automobile).

Fig. 1 schematically shows a side view of an example type of vehicle 1 in which the vehicle electrical system may be implemented. Here, the electric vehicle 1 is shown in the form of a car with front wheels 2a, rear wheels 2b, a passenger compartment 3, a luggage compartment and a vehicle power system comprising at least two

electric propulsion motors

5a, 5b, such as two multiphase alternating current motors or two direct current motors. The

electric machines

5a, 5b may for example be drive-connected to the front and rear axles, respectively, or to the right and left wheels of a common axis.

The vehicle powertrain further comprises an electrical storage system 6, such as a battery or a combination of batteries and capacitors, for propulsion of the vehicle. If the electric vehicle is a plug-in vehicle, i.e. configured for charging the electrical storage system by means of electrical energy from an external electrical grid, the vehicle may additionally comprise, for example, a terminal 7, which terminal 7 is configured for receiving an external charging connector for charging the electrical storage system. Advantageously, the terminal 7 is accessible from outside the vehicle 1. Alternatively, the terminal 7 may be a pad arranged for wireless reception/transmission of power (electricity) from/to an external power supply.

The vehicle powertrain may also include, for example, a combustion engine, a fuel cell, and the like.

Fig. 2 schematically illustrates a first example embodiment of a vehicle electrical system according to the present disclosure. Specifically, the vehicle electrical system may include: an electrical storage system 6; a first multiphase electric power machine 5a having a plurality of stator windings 8 connected in a star connection (manner) to a common neutral point 29a of the first multiphase electric power machine 5 a; a first inverter 9a operatively connected to the electrical storage system 6 and the first multiphase electrical machine 5a, wherein the first inverter 9a has a plurality of switch legs (switch legs) with switches; a second multiphase electric power machine 5b having a plurality of stator windings 13 connected in a star connection (manner) to a common neutral point 29b of the second multiphase electric power machine 5 b; a second inverter 9b operatively connected to the electrical storage system 6 and the second multi-phase electrical machine 5b, wherein the second inverter 9b has a plurality of switch leads with switches.

Thus, the plurality of

stator windings

8, 13 of each of the first and second

electric machines

5a, 5b are arranged in a star connection.

In other words, the first multiphase electric machine 5a has a plurality of stator windings 8 connected in a star to a first common neutral point 29a, and the second multiphase electric machine 5b has a plurality of stator windings 13 connected in a star to a second common neutral point 29 b.

The vehicle electrical system further includes a bi-directional buck-boost DC/DC converter 19, the bi-directional buck-boost DC/DC converter 19 being operatively connected to a common neutral point 29a of the first multi-phase electric machine 5a and a common neutral point 29b of the second multi-phase electric machine 5b and configured for using at least one stator winding 8, 13 of each of the first and second multi-phase

electric machines

5a, 5b as a buck-boost inductance.

The vehicle electrical system further includes: a bi-directional AC/DC converter operatively connected to the DC/DC converter 19 and the charging terminal 7 with or without passing through the intermediate electrical filter device 20; and an electronic control system 21 for controlling operation of the vehicle electrical system.

In order to charge the electrical storage system 6 of the vehicle electrical system with electric power from the vehicle external charging power source 17, a charging connector of the external charging power source 17 may be connected to the charging terminal 7 of the electrical storage system 6. Similarly, to power the vehicle external electrical load 18 with power from the electrical storage system 6, an electrical connector of the external electrical load 18 may be connected to the charging terminal 7 of the electrical storage system 6.

The first inverter 9a and the second inverter 9b are arranged for converting direct current received from the electrical storage system 6 into a multiphase alternating current of suitable frequency and/or amplitude for driving the first electrical machine 5a and the second electrical machine 5b, the first inverter 9a and the second inverter 9b may have various conventional circuit designs, for example one switch leg with two electronic power switches per phase.

According to some exemplary embodiments, electronic control system 21 is operably coupled to the switches of first inverter 9a and second inverter 9b and is configured to control the operation of the switches of first inverter 9a and second inverter 9b during a vehicle electrical storage system powered mode of operation (i.e., during an electric propulsion mode of operation) for controlling first and second multi-phase

electric machines

5a and 5b, respectively.

For example, the DC/DC converter 19 is a non-isolated switch mode DC-DC converter having a plurality of electronic power switches for providing a desired voltage level of boost or buck.

According to some exemplary embodiments, electronic control system 21 is operatively coupled to the switches of bi-directional DC/DC converter 19 and the switches of first inverter 9a and second inverter 9b, and is configured to control the operation of the switches of DC/DC converter 19, and possibly also first inverter 9a and/or second inverter 9b, according to a charging strategy, during a charging operation mode comprising the charging of electrical storage system 6, for converting the direct current supplied from AC/DC converter 20 into a modified direct current, and for supplying said modified direct current to electrical storage system 6 via the common

neutral points

29a, 29b of first and second multi-phase

electrical machines

5a, 5b.

In the charging operation mode, the corrected direct current is different from the direct current supplied from the AC/DC converter 20 in voltage level. In particular, during charging of the electrical storage system 6, the DC/DC converter operates as a buck converter (i.e. a voltage buck converter) when the inductance of the

stator windings

8, 13 is used as a buck inductance. Thus, the direct current supplied from the AC/DC converter 20 during charging of the electrical storage system 6 has a voltage level higher than that of the electrical storage system 6. This also enables Power Factor Correction (PFC), so that pf=1 can be achieved.

Furthermore, according to some exemplary embodiments, the electronic control system 21 is operatively coupled to the switches of the bi-directional DC/DC converter 19 and the switches of the first and

second inverters

9a, 9b, and is configured for controlling the operation of the switches of the first and/or

second inverters

9a, 9b and the DC/DC converter 19 during a vehicle-to-grid mode of operation (i.e. during an mode of operation comprising supplying electric power from the electric storage system 6 to the vehicle external electric load 18) for supplying direct current from the electric storage system 6 to the DC/DC converter 19 via the common

neutral points

29a, 29b of the first and second multi-phase

electric machines

5a, 5b, and for converting said direct current into a modified direct current for supplying to said AC/DC converter.

In the vehicle-to-grid mode of operation, the modified direct current differs from the direct current supplied from the electrical storage system 6 in voltage level. In particular, during a vehicle-to-grid mode of operation, when the inductance of the

stator windings

8, 13 is used as a boost inductance, the DC/DC converter operates as a boost converter (i.e. a voltage boost converter). Thus, the direct current supplied to the AC/DC converter 20 during the vehicle-to-grid mode of operation has a voltage level that is higher than the voltage level of the electrical storage system 6.

The bi-directional AC/DC converter 20 is an active single-phase or three-phase rectifier, also known as an active front-end rectifier. The bi-directional AC/DC converter 20 typically has series inductors connected in a single phase or in all three phases, and the sinusoidal source current is directly achieved by the high frequency switching of the AC/DC converter switches. The output DC voltage level is controlled, for example, by a Pulse Width Modulation (PWM) based high frequency switch of the AC/DC converter switch.

The AC/DC converter 20 and the DC/DC converter 19 may be assembled together, for example, on a grid front-end circuit board 55. Depending on the particular implementation, environment and overall circuit design, the circuit board may be located, for example, near the charging terminal 7. For the same reason, the first inverter 9a and the second inverter 9b may be assembled on a double-inverter circuit board, for example. Alternatively, the AC/DC converter 20, the DC/DC converter 19, and the first and

second inverters

9a and 9b may even be assembled on a common circuit board.

The electronic control system 21 may comprise separate hardware circuits, using software running in combination with a programmed microprocessor or general purpose computer, using one or more Application Specific Integrated Circuits (ASICs) and/or using one or more Digital Signal Processors (DSPs) for achieving the desired functions of the electrical system by controlling the switches of the

converters

19, 20 and the

inverters

9a, 9 b. The electronic control system 21, which is only schematically shown in the drawings, may have a centralized architecture, wherein a main controller submits instructions to sub-controllers via a data bus, and the electronic control system 21 is typically part of a larger electrical system comprising, for example, an electrical storage system controller or the like.

According to some exemplary embodiments, the electronic control system 21 is operatively coupled to the switches of the bi-directional AC/DC converter and is configured for controlling the operation of the switches of the AC/DC converter 20 for converting single-phase alternating current or multi-phase alternating current received from the vehicle external charging power source 17 via the charging terminal 7 into direct current for supply to said DC/DC converter during a vehicle charging mode of operation.

According to some exemplary embodiments, the electronic control system 21 is operatively coupled to the switch of the bi-directional AC/DC converter and is configured for controlling the operation of the switch of the AC/DC converter for converting the direct current received from said DC/DC converter 19 into single-phase alternating current or multi-phase alternating current for supplying the alternating current to the vehicle external electrical load 18 via the charging terminal 7 during a vehicle-to-grid operation mode.

The vehicle electrical system may be considered to include an electrical power system portion including the electrical storage system 6, the first and

second inverters

9a and 9b, and the first and second

electric machines

5a and 5b, and a grid-side charging/discharging portion including the DC/DC converter 19, the AC/DC converter 20, and the charging terminals 7.

Fig. 3 shows an exemplary embodiment of a more detailed implementation of the AC/DC converter, the DC/DC converter, the first inverter 9a and the second inverter 9b, and their internal relationship and connection to each other. The vehicle electrical system comprises a vehicle on-board electrical storage system 6 connected to a positive bus 52 and a negative bus 53, a first multi-phase electrical machine 5a having a plurality of stator windings 8, a first inverter 9a connected to the electrical storage system 6 and the first multi-phase electrical machine 5a, a second multi-phase electrical machine 5b having a plurality of stator windings 13, a second inverter 9b connected to the electrical storage system 6 and the second multi-phase electrical machine 5b, wherein the first inverter 9a has a plurality of switch leads 10, 11, 12 with

switches

10a, 10b, 11a, 11b, 12a, 12b, and the second inverter 9b has a plurality of switch leads 14, 15, 16 with

switches

14a, 14b, 15a, 15b, 16a, 16 b.

The electrical storage system 6 may comprise a high voltage battery composed of, for example, lithium ion battery cells, lithium sulfur battery cells, or solid state battery cells, among others. The high voltage battery may, for example, have a rated voltage level in the range of 100V-1500V. The battery capacity in kWh depends on factors such as whether the vehicle is a hybrid vehicle with an additional power source (e.g., a combustion engine), or whether the vehicle is a pure electric vehicle, and the desired operating range. The capacity may be, for example, about 10-150kWh.

However, in certain applications, such as, for example, so-called "light-mix" systems, the electrical storage system 6 may comprise a nominal output voltage of the battery, for example, of about 24V-59V, in particular 24V or 48V.

The first and second multi-phase

electric machines

5a, 5b may be, for example, three-phase, five-phase, or seven-phase electric machines, or the like. For example, a three-phase electric machine may have three stator windings, each winding component being arranged in two halves on opposite sides in the stator. The three stator windings may then be disposed 120 degrees apart from each other, and each stator winding may then be considered to have two poles, i.e., a three-phase two-pole electric machine. However, the stator winding may alternatively be divided into four sections, wherein the sections are shifted 90 degrees from each other. Such stator windings are considered to have four poles, namely three-phase four-pole electric machines. Other stator winding arrangements are also possible, such as a hexapole arrangement, etc.

The first electric machine 5a and the second electric machine 5b may be, for example, permanent magnet synchronous motors or alternating current induction motors or switched reluctance motors.

In the example embodiment described with reference to fig. 3, each of the first inverter 9a and the second inverter 9b has three switch leads, namely a

first switch lead

10, 14, a

second switch lead

11, 15 and a

third switch lead

12, 16, all of which are connected in parallel between the positive and

negative bus bars

52, 53. Each of the

switch legs

10, 11, 12, 14, 15, 16 of the first and

second inverters

9a, 9b is supplied with direct current from the electrical storage system 6, and the control system may then control the switches to perform an appropriate switching operation of the

inverter switches

10a, 10b, 11a, 11b, 12a, 12b, 14a, 14b, 15a, 15b, 16a, 16b for providing a phase shifted output voltage, such as, for example, a substantially three-phase sinusoidal characteristic, to the

stator windings

8, 13 of the first and second

electrical machines

5a, 5 b.

Each

switch lead

10, 11, 12, 14, 15, 16 may have two switches, for example a

first switch

10a, 11a, 12a, 14a, 15a, 16a and a

second switch

10b, 11b, 12b, 14b, 15b, 16b. The first stator winding 8a of the first electric machine 5a may be connected to the first switch lead 10 between the first switch 10a and the second switch 10b of the first inverter 9a, the second stator winding 8b of the first electric machine 5a may be connected to the second switch lead 11 between the first switch 11a and the second switch 11b of the first inverter 9a, and the third stator winding 8c of the first electric machine 5a may be connected to the third switch lead 12 between the first switch 12a and the second switch 12b of the first inverter 9 a. Also, the first stator winding 13a of the second electric machine 5b may be connected to the first switch lead 14 between the first switch 14a and the second switch 14b of the second inverter 9b, the second stator winding 13b of the second electric machine 5b may be connected to the second switch lead 15 between the first switch 15a and the second switch 15b of the second inverter 9b, and the third stator winding 13c of the second electric machine 5b may be connected to the third switch lead 16 between the first switch 16a and the second switch 16b of the second inverter 9 b.

However, other inverter designs are possible within the scope of the present application.

The

switches

10a, 10b, 11a, 11b, 12a, 12b, 14a, 14b, 15a, 15b, 16a, 16b may be, for example, power transistors for controlling the torque and/or speed of the first and second multi-phase electric machines. For example, the switch may be an Insulated Gate Bipolar Transistor (IGBT) or a MOSFET.

Each of the

switches

10a, 10b, 11a, 11b, 12a, 12b, 14a, 14b, 15a, 15b, 16a, 16b of the first inverter 9a and the second inverter 9b is provided with a parallel-connected reverse diode, also called freewheeling diode, body diode or absorption diode. The reverse diode may be, for example, an intrinsic diode, i.e., a reverse diode function. For example, MOSFET type transistors typically include an intrinsic reverse diode function due to their design and structure. However, some IGBTs typically do not have such an intrinsic reverse diode, but instead are provided with an extrinsic reverse diode, i.e. a physically independent diode separate from and connected in parallel with the transistor. In addition, the MOSFET transistor may also be provided with an extrinsic reverse diode. A reverse diode is typically required to avoid situations where a large negative voltage may build up on the transistor when switching the inductive load, as the inductive load typically generates a large negative voltage during negative current changes, which in turn may destroy the transistor.

The dc link capacitor 54 may be connected between the positive bus 53 and the negative bus 54.

In the exemplary embodiment of fig. 3, the bi-directional buck/boost DC/DC converter is a non-isolated switching converter having two bi-directional switching devices, namely a first bi-directional switching device 30 and a second bi-directional switching device 31. Furthermore, the bi-directional buck/boost DC/DC converter relies on the inductance of one or

more stator windings

8, 13 of each of the first and second multi-phase

electric machines

5a, 5b as an energy storage element for achieving voltage buck during the vehicle charging mode and voltage boost during the vehicle to grid mode of operation.

The first bi-directional switching means 30 may for example comprise a first electronic switch 56 connected in series with a second electronic switch 57, the second electronic switch 57 being oriented opposite to the first electronic switch 56. In other words, the collector terminals of the first electronic switch 56 and the second electronic switch 57 may be connected to each other, or the emitter terminals of the first electronic switch 56 and the second electronic switch 57 may be connected to each other. The second bi-directional switching device 31 may have the same design, i.e. the first electronic switch 58 is connected in series with and opposite to the second electronic switch 59.

Each of the switches 56-59 of the first and second bi-directional switching means 30, 31 may be provided with a parallel connected reverse diode.

In the exemplary embodiment of fig. 3, the AC/DC converter 20 has a grid side with two connection points 61, 62 for receiving single-phase alternating current from the charging terminal 7 and outputting single-phase alternating current to the charging terminal 7, and an electric machine side with a first connection point 63 and a second connection point 64 for receiving direct current from the DC/DC converter 19 and outputting direct current to the DC/DC converter 19.

The first bi-directional switching device 30 of the DC/DC converter 19 is operatively connected to the first connection point 63 of the AC/DC converter 20 and the common neutral point 29a of the first multi-phase electric machine 5 a. Furthermore, the first bi-directional switching device 30 of the DC/DC converter 19 is configured for selectively opening and closing an electrical connection between the first connection point 63 of the AC/DC converter 20 and the common neutral point 29a of the first multi-phase electric machine 5a for controlling the current between said

points

63 and 29a.

The second bi-directional switching device 31 is operatively connected to the common

neutral points

29a, 29b of the first and second multi-phase

electric machines

5a, 5b and is configured for selectively opening and closing an electrical connection between the common neutral points of the first and second multi-phase

electric machines

5a, 5 b.

Furthermore, the second connection point 64 of the AC/DC converter 20 may be permanently (fixedly) electrically connected with the common neutral point 29b of the second multi-phase electric machine 5 b.

The electrical connection extending from the common neutral point 29a of the first multi-phase electric machine 5a to the common neutral point 29b of the second multi-phase electric machine 5b via the second bi-directional switching device 31 may be devoid of any substantial inductor. This means that no inductive electrical element for achieving the desired voltage step-down conversion is needed in the electrical connection extending between the common

neutral points

29a, 29 b. On the other hand, if an inductive element is included in the electrical connection extending between the common

neutral points

29a, 29b, its inductance level may be relatively small, for example less than 25%, in particular less than 10%, of the inductance of a single stator winding of either of the first and second multi-phase

electric machines

5a, 5b, in order to avoid excessive weight.

Further, the vehicle electrical system may have no DC/DC converter in the electric power supply path extending between the electrical storage system 6 and any one of the first inverter 9a and the second inverter 9 b. This has the advantage that expensive high power switches associated with e.g. 50-200kW DC/DC converters located in the power system are avoided compared to e.g. 5-20kW DC/DC charging converters arranged outside the drive train.

In the exemplary embodiment of fig. 3, the AC/DC converter 20 is a single-phase active front-end rectifier comprising a plurality of

switch legs

65, 66 connected between a positive bus associated with a first connection point 63 of the AC/DC converter 20 and a negative bus associated with a second connection point 64 of the AC/DC converter 20, wherein each switch leg has at least two

switches

65a, 65b, 66a, 66b connected in series via an intermediate conductor. The AC/DC converter 20 may further include a direct current link capacitor 67 disposed between the first connection point 63 and the second connection point 64.

The grid side of the AC/DC converter 20 comprises two connection points 61, 62 electrically connected to the charging terminal 7 for receiving single-phase alternating current (i.e. phase and neutral) from the vehicle external charging source 17 or outputting single-phase alternating current to the vehicle external electrical load, wherein each of the two connection points is electrically connected to a separate intermediate conductor of the plurality of switch leads 65, 66, and wherein the phase line comprises an inductor element 69 located between the first connection point 61 and the first switch lead 65.

For charging of the electrical storage system 6 of the vehicle electrical system according to fig. 3, the charging connector 68 of the external alternating current charging source 17 may be connected to the charging terminal 7 of the vehicle electrical system. The charging source 17 may, for example, supply 240V single-phase alternating current and the electrical storage system 6 may, for example, have a nominal voltage level of 200V.

To reduce the charging voltage level, the control system 21 is configured to be able to operate the first 30 and second 31 bidirectional switching devices of the DC/DC converter 19 in synchronized and alternating on and off cycles. Hereby a direct and easy to implement step-down solution is achieved, which can also be implemented without changing or customizing the inverter and/or the electric machine, and without requiring a DC/DC converter within the power system.

Fig. 4 schematically shows how the first and second

bi-directional switching devices

30, 31 may be operated with synchronized alternating on and off periods, wherein the first bi-directional switching device 30 is turned on during a first phase, time period t1, and then turned off during a second phase, time period t 2.

the ratio of t1 to t_tot is referred to as the duty cycle of the DC/DC converter and controls the voltage step-down level. The second bi-directional switching device 31 may operate substantially opposite to the first bi-directional switching device 30 such that the second bi-directional switching device 31 is turned off during the first phase (period) t1 and then turned on during the second phase (period) t 2. The switching rate (i.e., switching frequency) is equal to 1/t_tot.

Fig. 5A and 5B show a first exemplary embodiment of the current path during said alternating on and off periods during charging of the electrical storage system 6. Some of the switches of the first inverter 9a and the second inverter 9b may also be controlled in a synchronized manner with the switches 56-69 of the DC/DC converter 19 for obtaining a beneficial effect on the charging behaviour of the vehicle electrical system.

In particular, the inductance of each individual stator winding 8, 13 of the first and second

electric machines

5a, 5b generally depends on the angular position of the rotor within the

electric machines

5a, 5 b. At a particular angular position of the electric machine, the inductance of the stator winding with the largest inductance may be, for example, approximately 1.5-2 times the inductance of the stator winding with the smallest inductance. Each of the first and second

electric machines

5a, 5b may be equipped with a rotor angular position sensor for identifying the angular position of the rotor and thus for determining the inductance of the respective stator winding at the current angular position.

Thus, by appropriate control of the switches 10a-12b, 14a-16b of the first inverter 9a and the second inverter 9b, the route of the charging current may be through a specific stator winding of the first electric machine 5a and/or the second electric machine 5b, or through all stator windings of the first electric machine 5a and/or the second electric machine 5 b. Thus, the total inductance l_tot of the charging circuit can be selected according to the environment. The total inductance l_tot of the two separate series-connected inductances L1, L2 can be determined as: l (L) _tot =l1+l2, and the total inductance l_tot of the three individual parallel connected inductances L1, L2, L3 can be determined as:

furthermore, as the switching rate increases, the level of inductance required to operate the buck converter decreases. Thus, at least two parameters may be controlled during, for example, battery buck charging to achieve desired results in terms of efficiency, harmonic noise, current ripple, etc., i.e., switching rate and circuit inductance level.

These two parameters generally have the following effects:

other factors that may influence the switching frequency and the selection of the total inductance l_tot may be, for example, supply voltage level, battery SoC, battery health, battery temperature, etc.

Referring again to fig. 5A, the current path during the first phase of the charging mode of operation is shown. For example, if a high inductance is required in this particular charging occasion and the control system 21 determines that the third stator winding 13c of the second electric machine 5b is the highest of the three

inductances

13a, 13b, 13c of the second electric machine 5b based on the angular position obtained by the rotor of the second electric machine 5b detected by the associated angular position sensor or the like, the first switch 16a of the third switch lead 16 of the second inverter 9b may be set to a closed state (i.e. conductive state) for routing the charging current through the third stator winding 13c of the second electric machine 5b during the first phase associated with the energy charging of the buck inductance. All other switches of the first inverter 9a and the second inverter 9b may be set to an off state (i.e., a non-conductive state).

Further, the second switch 57 of the first bidirectional switch device 30 is set to the closed state, the first bidirectional switch device 30 is set to the conductive state, and the second bidirectional switch device 31 is set to the nonconductive state. Thus, during a first phase corresponding to the charging of the buck inductor, the direct charging current supplied by the AC/DC converter 20 is routed through the following components: the second switch 57 of the first bi-directional switching device 30, the intrinsic or extrinsic reverse diode of the first switch 56 of the first bi-directional switching device 30, the entire winding 8 of the first electric machine 5a and the associated intrinsic or extrinsic reverse diode of the first switch 10a-12a of the second and third switch leads 10-12, the first switch 16a of the third switch lead of the second inverter 9b, the third stator winding 13c of the second electric machine 5b, and back to the AC/DC converter 20.

The charging current through the first winding 8a, the second winding 8b and the third winding 8c of the first electric machine 5a will depend on the instantaneous inductance of said windings.

Referring again to fig. 5B, the current path during the second phase of the charging mode of operation is shown. At this stage, all switches of the first inverter 9a and the second inverter 9b may be set to an off state. Further, the first bidirectional switch device 30 is set to a non-conductive state, and the second bidirectional switch device 31 is set to a conductive state by setting the second switch 59 of the second bidirectional switch device 31 to a closed state.

As a result, the energy stored in the form of a magnetic field in the stator winding is released and drives a charging current in the closed path, which current has the same direction as the charging current during the first phase. In particular, the charging current is routed through the following components: the electrical storage system 6, the intrinsic or extrinsic reverse diode of the second switch 16b of the third switch leg of the second inverter 9b, the third stator winding 13c of the second electrical machine 5b, the second switch 59 of the second bi-directional switching device 31, the intrinsic or extrinsic reverse diode of the first switch 58 of the second bi-directional switching device 31, all windings 8 of the first electrical machine 5a and the associated intrinsic or extrinsic reverse diode of the first switch leg of the first inverter 9a, the second switch leg, the first switch 10a-12a of the third switch leg 10-12, and back to the electrical storage system 6.

It is clear that if another inductance level is desired, the control system 21 may determine another combination of stator windings 13 of the second electric machine 5b to be used based on the angular position obtained by the rotor of the second electric machine 5b detected by the associated angular position sensor or the like, and control the associated first switches 14a-16a of the second inverter 9b accordingly.

In fig. 5A and 5B, the switches set to the closed (conductive) state are marked with circles.

The direct current through some or all of the stator windings in the first and second

electric machines

5a, 5b does not cause any substantial (significant) rotational torque of the rotor, except for some initial small angular movements of the direct current charging current that may be used to adjust the rotor to the selected winding and/or small vibrations caused by current ripple, etc. However, these types of small initial angular movements and/or vibrations may typically be eliminated by braking the rotor or associated wheels during the charging mode of operation and the vehicle-to-grid mode of operation. For example, braking may be achieved by conventional friction brakes associated with vehicle wheels.

Fig. 6A and 6B show a second exemplary embodiment of the current path during the alternating on and off cycles during charging of the electrical storage system 6.

For example, if a high inductance is required in this particular charging occasion and the control system 21 determines that the third stator winding 8c of the first electric machine 51 has the highest of the three

inductances

8a, 8b, 8c of the first electric machine 5a and possibly greater than any of the inductances of the windings 13 of the second electric machine 5b based on the angular position obtained by the rotor of the first electric machine 5a detected by the associated angular position sensor or the like, the second switch 12b of the third switch lead 12 of the first inverter 91 may be set to a closed state (i.e. a conductive state) for routing of the charging current through the third stator winding 8c of the first electric machine 5a during the first phase. All other switches of the first inverter 9a and the second inverter 9b may be set to an off state (i.e., a non-conductive state).

Further, by setting the second switch 57 of the first bidirectional switch device 30 to the closed (conductive) state, the first bidirectional switch device 30 is set to the conductive state, and the second bidirectional switch device 31 is set to the nonconductive state. Thus, during a first phase corresponding to the charging of the buck inductor (stator winding), the direct charging current supplied by the AC/DC converter 20 is routed through the following components: the second switch 57 of the first bi-directional switching device 30, the intrinsic or extrinsic reverse diode of the first switch 56 of the first bi-directional switching device 30, the third stator winding 8c of the first electric machine 5a, the second switch 12b of the third switch lead 12 of the first inverter 9a, the first switch lead of the second inverter 9b, the intrinsic or extrinsic reverse diode of the second switches 14b-16b of the second and third switch leads 14-16, the complete winding 13 of the second electric machine 5b, and back to the AC/DC converter 20.

Referring to fig. 6B, the current path during the second phase of the charging mode of operation is shown. In the second stage, all switches of the first inverter 9a and the second inverter 9b may be set to an off state. Further, the first bidirectional switch device 30 is set to a non-conductive state, and the second bidirectional switch device 31 is set to a conductive state by setting the second switch 59 of the second bidirectional switch device 31 to a closed state.

As a result, the energy stored in the form of a magnetic field in the

stator windings

8c, 13a, 13b, 13c is released and drives a charging current in a closed path, which current has the same direction as the charging current during the first phase. In particular, the charging current is routed through the following components: the electrical storage system 6, the associated intrinsic or extrinsic reverse diodes of the first switch leg of the second inverter 9b, the second switch leg and the second switch leg 14b-16b of the third switch leg 14-16, the entire winding 13 of the second electrical machine 5b, the second switch 59 of the second bi-directional switching device 31, the intrinsic or extrinsic reverse diode of the first switch 58 of the second bi-directional switching device 31, the third stator winding 8c of the first electrical machine 5a, the intrinsic or extrinsic reverse diode of the first switch 12a of the third switch leg 12 of the first inverter 9a, and back to the electrical storage system 6.

Still alternatively, if the highest possible buck inductance may not be needed, while other aspects are considered more relevant (such as, for example, eliminating the need to operate the switches of the first inverter 9a and the second inverter 9B during charging), the following charging strategy described with reference to fig. 7A and 7B may be selected.

Here, during the first phase and the second phase, all the switches of the first inverter 9a and the second inverter 9b may be set to an off state (i.e., a non-conductive state).

Further, during the first phase, the first bidirectional switch device 30 is set to the conductive state and the second bidirectional switch device 31 is set to the non-conductive state by setting the second switch 57 of the first bidirectional switch device 30 to the closed (conductive) state. Thus, during a first phase corresponding to the charging of the buck inductor (stator winding), the route of the direct charging current supplied by the AC/DC converter 20 is as shown in fig. 7A, through the following components: the second switch 57 of the first bi-directional switching device 30, the intrinsic or extrinsic reverse diode of the first switch 56 of the first bi-directional switching device 30, the entire winding 8 of the first electric machine 5a and the associated intrinsic or extrinsic reverse diode of the first switch 10a-12a of the second and third switch leads 10-12, the intrinsic or extrinsic reverse diode of the second switch 14b-16b of the second and third switch leads 14-16, the entire winding 13 of the second electric machine 5b of the second and third switch leads 10-12, the electrical storage system 6, the first switch lead of the second inverter 9b, and the return to the AC/DC converter 20.

Referring to fig. 7B, the current path during the second phase of the charging mode of operation is shown. In the second phase, the first bi-directional switching device 30 is set to a non-conductive state and the second bi-directional switching device 31 is set to a conductive state by setting the second switch 59 of the second bi-directional switching device 31 to a closed state. As a result, the energy stored in the form of a magnetic field in the

stator windings

8, 13 is released and drives a charging current in the closed path, which current has the same direction as the charging current during the first phase. Specifically, the charging current is routed through the following elements: the electrical storage system 6, the first switch leg of the second inverter 9b, the associated intrinsic or extrinsic reverse diodes of the second switches 14b-16b of the second and third switch legs 14-16, the entire winding 13 of the second electrical machine 5b, the second switch 59 of the second bi-directional switching device 31, the intrinsic or extrinsic reverse diodes of the first switch 58 of the second bi-directional switching device 31, the entire winding 8 of the first electrical machine 5a, and the associated intrinsic or extrinsic reverse diodes of the first switch legs of the first inverter 9a, the second switch leg, and the first switches 10a-12a of the third switch legs 10-12, and back to the electrical storage system 6.

Thereby, the operation of the buck converter and the charging of the electrical storage system are completed without utilizing synchronous switching of the switches of the first inverter 9a and the second inverter 9b, so that it is possible to reduce the loss associated with the switching of the switches of the first inverter 9a and the second inverter 9b and to avoid a temperature rise. The switching frequency during buck charging is, for example, in the range of 1kHz-1 MHz.

In other words, during a vehicle charging mode of operation, the control system 21 may be configured to operate the DC/DC converter 19 in a voltage step-down mode comprising controlling each of the first and second

bidirectional switch devices

30, 31 to have alternating on and off periods such that, during a first phase involving charging the energy of the step-down inductance, current is able to flow from the first connection point 63 of the AC/DC converter 20, via the first bidirectional switch device 30, the one or more stator windings 8 of the first multi-phase electric 5a, the first inverter 9a, the second inverter 9b (via simultaneous bypass or non-bypass at the first few places to the electrical storage system 6), the one or more stator windings 13 of the second multi-phase electric machine 5b, and back to the second connection point 64 of the AC/DC converter 20 when the first bidirectional switch device 30 is on and the second bidirectional switch device 31 is off.

Further, during a vehicle charging mode of operation, the control system 21 may be configured to operate the DC/DC converter 19 in a voltage step-down mode comprising controlling each of the first and second

bidirectional switching devices

30, 31 to have alternating on and off periods such that, during a second phase involving discharging energy of the step-down inductance, charging current is enabled from the negative pole of the electrical storage system 6 via the second inverter 9b, the one or more stator windings 13 of the second multi-phase electrical machine 5b, the second bidirectional switching device 31, the one or more stator windings 8 of the first multi-phase electrical machine 5a, the first inverter 9a, and back to the positive terminal of the electrical storage system 6 when the first bidirectional switching device 30 is off and the second bidirectional switching device 31 is on.

Further, during the vehicle charging mode of operation, the control system 21 is configured to operate the DC/DC converter with a voltage step-down involving operating the first bidirectional switching device 30 with a first set of alternating on and off periods and operating the second bidirectional switching device 31 with a second set of alternating on and off periods that are set to be synchronized and inverted relative to the first set of alternating on and off periods.

As described with reference to fig. 3 and 5A-7B, each of the first inverter 9a and the second inverter 9B includes at least one inverter leg 10-12, 14-16 for each phase (winding) of the associated multi-phase electric machine, and each inverter leg 10-12, 14-16 includes an upper switch 10a-12a, 14a-16a associated with a positive dc bus 52, the upper switches 10a-12a, 14a-16a being connected in series with a lower switch 10B-12B, 14B-16B associated with a negative dc bus 53.

Further, the control system 21 may be configured to set all of the upper and lower switches of the first and

second inverters

9a, 9b to an open (non-conductive) state during both the first and second phases during the vehicle charging operation mode. Alternatively, the control system 21 may be configured to set all upper and lower switches of the first inverter 9a and all lower switches of the second inverter 9b to an open state during both the first phase and the second phase, and to set one, two, three or more upper switches 14a-16a of the second inverter 9b to a closed state during the first phase, and to set all upper switches of the second inverter 9b to an open state during the second phase, during the vehicle charging operation mode.

Still alternatively, the control system 21 may be configured to set all upper and lower switches of the second inverter 9b and all upper switches of the first inverter 9a to an open state during the first phase, to set one, two, three or more lower switches of the first inverter 9a to a closed state during the first phase, and to set all lower switches of the first inverter 9a to an open state during the second phase, during the vehicle charging operation mode.

The vehicle electrical system according to the present disclosure is also capable of operating in a vehicle-to-grid mode of operation, which means that during a vehicle stationary state, power is supplied from the electrical storage system 6 to the external electrical load 18. This is suitable, for example, for balancing the power grid in case of sudden changes in demand.

One exemplary embodiment for controlling the vehicle electrical system during a vehicle-to-grid mode of operation is described below with reference to fig. 8A and 8B. In particular, in a vehicle-to-grid mode of operation, if the voltage level provided by the electrical storage system is too low compared to the required voltage level, the DC/DC converter is configured to operate in a boost mode.

In boost mode, the first and second

bidirectional switching devices

30, 31 of the DC/DC converter 19 may operate in synchronous alternating on and off periods, as described above with reference to fig. 4, wherein the first bidirectional switching device 30 is turned on during a first phase (period) t1 and then turned off during a second phase (period) t 2. the ratio of t1 to t_tot is referred to as the duty cycle of the DC/DC converter and controls the voltage boost level. The second bi-directional switching device 31 may operate substantially opposite to the first bi-directional switching device 30 such that the second bi-directional switching device 31 is turned off during the first phase (period) t1 and then turned on during the second phase (period) t 2.

As described above, the appropriate boost inductance level and boost switching frequency of the stator winding may be selected first. Thereafter, the inductance level of the

various stator windings

8, 13 of the first and second

electric machines

9a, 9b may be determined based on the angular position detection of the associated rotor, and an appropriate combination of

stator windings

8, 13 may be selected for the vehicle-to-grid mode of operation by setting the corresponding switches 10a-12a, 14b-16b to an open or closed mode.

For example, if a high inductance is desired during a particular vehicle-to-grid operation scenario and the control system 21 determines that the third stator winding 8c of the first electric machine 5a has the highest of the three

inductances

8a, 8b, 8c of the first electric machine 5a and the first stator winding 13a of the second electric machine 5b has the highest of the three

inductances

13a, 13b, 13c of the second electric machine 5b based on the angular positions obtained by the rotors of the first electric machine 5a and the second electric machine 5b detected by the associated angular position sensors or the like, the control system may choose to use them for the

stator windings

8c, 13a for providing the desired boost inductance.

Thus, during the following first and second phases of vehicle-to-grid operation, the first switch 12a of the third switch lead 12 of the first inverter 9a is set to a closed state (i.e. conductive state) and the second switch 14b of the first switch lead 14 of the second inverter 9b is set to a closed state (i.e. conductive state), thereby enabling the routing of the discharge current of the vehicle to the grid through the third stator winding 8c of the first electric machine 5a and through the first winding 13a of the second electric machine 9 b. During the first and second phases, all other switches of the first and

second inverters

9a and 9b may be set to an off state (i.e., a non-conductive state).

Referring to fig. 8A, during the first phase, the second bi-directional switching device 31 is set to the conductive state by setting the first switch 58 of the second bi-directional switching device 31 to the closed (conductive) state, and the first bi-directional switching device 30 is set to the non-conductive state. Thus, during a first phase corresponding to the charging of the boost inductance (stator winding), the direct-current discharge current supplied by the electrical storage system 6 is routed through the following components: the first switch 12a of the third switch lead 12 of the first inverter 9a, the third stator winding 8c of the first electric machine 5a, the first switch 58 of the second bi-directional switching device 31, the intrinsic or extrinsic reverse diode of the second switch 59 of the second bi-directional switching device 31, the first winding 13a of the second electric machine 5b, the second switch 14b of the first switch lead 14 of the second inverter 9b, and back to the electric storage system 6.

Referring to fig. 8B, which shows the current path during the second phase of the vehicle to grid mode of operation, the switches of the first inverter 9a and the second inverter 9B remain the same as during the first phase, but the second bi-directional switching device 31 is set to a non-conductive state, and the first bi-directional switching device 30 is set to a conductive state by setting the first switch 56 of the first bi-directional switching device 30 to a closed state.

As a result, the energy stored in the form of a magnetic field in the

stator windings

8c, 13a is released and drives the vehicle to the current of the grid, which current has the same direction as the discharge current during the first phase. In particular, the route of the current of the vehicle to the grid: from the external electrical load 18 via the AC/DC converter through the following components: the first winding 13a of the second electric machine 5b, the second switch 14b of the first switch lead 14 of the second inverter 9b, the electrical storage system 6, the first switch 12a of the third switch lead 12 of the first inverter 9a, the third stator winding 8c of the first electric machine 5a, the first switch 56 of the first bi-directional switching device 30, the intrinsic or extrinsic reverse diode of the second switch 57 of the first bi-directional switching device 30.

Obviously, if another level of boost inductance is required, another combination of

stator windings

8, 13 may be selected by appropriate control of the switches of the first and second

electric machines

9a, 9 b.

In other words, the control system 21 is configured to operate the DC/DC converter with a voltage boost during a vehicle-to-grid mode of operation, the voltage boost comprising controlling each of the first and second

bidirectional switching devices

30, 31 to have alternating on and off periods, such that during the first phase, when the first bidirectional switching device 30 is off and the second bidirectional switching device 31 is on, current is able to flow from the positive pole of the electrical storage system 6, via the first inverter 9a, the one or more stator windings 8 of the first multi-phase electrical machine 5a, the second inverter 9b, the one or more stator windings 13 of the second multi-phase electrical machine 5b, back to the negative terminal of the electrical storage system 6.

Furthermore, the control system 21 is also configured such that during the second phase, when the first bi-directional switching device 30 is on and the second bi-directional switching device 31 is off, current can flow from the second connection point 64 of the AC/DC converter 20, via the one or more stator windings 13 of the second multi-phase electric machine 5b, the second inverter 9b, the electrical storage system 6, the first inverter 9a, the one or more stator windings 8 of the first multi-phase electric machine 5a, the first bi-directional switching device 30, and back to the first connection point 63 of the AC/DC converter 20.

Furthermore, each of the first inverter 9a and the second inverter 9b comprises at least one inverter leg 10-12, 14-16 for each

phase

8, 13 of the associated multiphase

electrical machine

5a, 5b, and each inverter leg 10-12, 14-16 comprises an upper switch 10a-12a, 14a-16a associated with the positive direct current bus 52, which upper switch 10a-12a, 14a-16a and a lower switch 10b-12b, 14b-16b associated with the negative direct current bus 53 are connected in series, and the control system 21 is configured for setting one, two, three or more upper switches 10a-12a of the first inverter 9a to a closed state during both the first phase and the second phase, setting one, two, three or more lower switches 14b-16b of the second inverter 9b to a closed state during both the first phase and the second phase, and setting all the upper switches 10a-12 a-16b of the second inverter 9b to an open state during both the first phase and the second phase, respectively, during the vehicle to the grid mode of operation.

As described above, according to some exemplary embodiments, the control system 21 may be configured to control the switches 10a-12b, 14a-16b of the first inverter 9a and/or the second inverter 9b based on the angular position of the rotor of the first multi-phase electric machine 5a and/or the second multi-phase electric machine 5b during a vehicle-to-grid operation mode and/or a vehicle charging operation mode.

Furthermore, according to some exemplary embodiments, control system 21 is configured to select which of the one or more upper switches 10a-12a of first inverter 9a and which of the one or more lower switches 14b-16b of second inverter 9b should be set to a closed state during the first phase and the second phase based on an angular position of a rotor of first multiphase electrical machine 5a and/or second multiphase electrical machine 5b during a vehicle-to-grid mode of operation.

Furthermore, according to some exemplary embodiments, control system 21 is configured to select which of the one or more upper switches 14a-16a of second inverter 9b should be set to the closed state during the first phase or which of the one or more lower switches 10b-12b of first inverter 9a should be set to the closed state during the first phase, based on the angular position of the rotor of first and/or second multi-phase

electric machine

5a, 5b during the vehicle charging mode of operation.

According to some exemplary embodiments, the control system 21 is configured for selecting which of the one or more upper switches 10a-12a of the first inverter 9a and which of the one or more lower switches 14b-16b of the second inverter 9b should be set to a closed state during the first phase and the second phase during the vehicle-to-grid operation mode based on the estimated or calculated maximum current of the switches of the first inverter 9a and/or the second inverter 9 b.

Similarly, according to some exemplary embodiments, the control system 21 is configured to select which of the one or more upper switches 14a-16a of the second inverter 9b should be set to the closed state during the first phase or which of the one or more lower switches 10b-12b of the first inverter 9a should be set to the closed state during the first phase during the vehicle charging mode of operation based on the estimated or calculated maximum current of the switches of the first inverter 9a and/or the second inverter 9 b.

Fig. 9 shows the same vehicle electrical system as described above with reference to fig. 1 to 8B, but here with some additional electrical filter means as an interface (means) between the AC/DC converter 20 and the charging terminal 7. Specifically, the LCL filter device 70 has a grid-side inductor 71 connected in series with a converter-side inductor 72 in a single-phase line, and a capacitor 73 connected between the grid-side inductor 71 and the converter-side inductor 72 and connected to a neutral line. Furthermore, a further filter device 75 with a common mode filter and with EMC protection may be arranged in series with the LCL filter device 70. Both the EMC filter device 75 and the LCL filter device 70 are preferably arranged on a grid front-end circuit board 55 with a connection interface 76 for electrical connection with the charging terminals 7.

Fig. 10 schematically shows a version of a vehicle electrical system adapted to be charged with three-phase alternating current during vehicle charging and to supply three-phase alternating current during vehicle-to-grid operation. The vehicle electrical system of fig. 10 is identical in structure and function to the system described above with reference to fig. 1-8B, except that the AC/DC converter is provided with an additional switch lead 77.

In other words, the AC/DC converter 20 herein is a three-phase active front-end rectifier comprising a plurality of switch leads 65, 66, 77 connected between a positive bus associated with the first connection point 63 of the AC/DC converter 20 and a negative bus associated with the second connection point 64 of the AC/DC converter 20, wherein each

switch lead

65, 66, 77 has at least two

switches

65a, 65b, 66a, 66b, 77a, 77b connected in series via an intermediate conductor. The grid side of the AC/DC converter 20 comprises three connection points 78-80 electrically connected to the charging terminals 7 for receiving three-phase alternating current from the three-phase vehicle external charging source 17 or outputting three-phase alternating current to the vehicle external electrical load, wherein each of the three connection points 78-80 is electrically connected to a separate intermediate conductor of the plurality of switch leads 65, 66, 77, and wherein each phase line (line or wire) comprises an inductor element 69 between the associated connection point 78-80 and the

switch lead

65, 66, 77.

Fig. 14 shows the same vehicle electrical system as described above with reference to fig. 10, but here with some additional three-phase electrical filter means as an interface between the AC/DC converter 20 and the charging terminals 7. Specifically, the LCL filter device 70 has a grid-side inductor connected in series with a converter-side inductor in each phase line, and has a capacitor connected between the grid-side inductor 71 and the converter-side inductor 72 and connected to a neutral point. Furthermore, a further filter device 75 with EMC protection and with a common mode filter may be arranged in series with the LCL filter device 70. Both the EMC filter device 75 and the LCL filter device 70 are preferably arranged on a grid front-end circuit board 55 with a connection interface 76 for electrical connection with the charging terminals 7.

Fig. 15 shows a notable and advantageous aspect of the vehicle electrical system according to the present disclosure, i.e. the multi-phase arrangement of the vehicle electrical system may be connected to a single-phase external load 17 without requiring any change in the hardware settings of the vehicle electrical system. In other words, the vehicle electrical system according to the present disclosure is not only capable of being connected to a wide range of different alternating current voltage levels, but is also capable of being connected to a different number of phases, and all without requiring hardware changes to achieve this.

The invention also relates to a vehicle comprising a vehicle electrical system as described above with reference to fig. 1-10 and 14-15 or as described with reference to the appended claims.

The present disclosure also relates to a method for charging an electrical storage system 6 of a vehicle electrical system. The main steps of the method will be described below with reference to fig. 11. The method comprises a first step S1: the first inverter 9a is connected to the electrical storage system 6 and to the first multi-phase electrical machine 5a, which first multi-phase electrical machine 5a has a plurality of stator windings 8 connected to a common neutral point, wherein the first inverter 9a has a plurality of switch leads 10, 11, 12 with

switches

10a, 10b, 11a, 11b, 12a, 12 b. The method further comprises a second step S2: the second inverter 9b is connected to the electrical storage system 6 and to a second multiphase electrical machine 5b having a plurality of stator windings 13 connected to a common neutral point, wherein the second inverter 9b has a plurality of switch leads 14, 15, 16 with

switches

14a, 14 b. Furthermore, the method comprises a third step S3: the bi-directional buck-boost DC/DC converter is connected to a common neutral point of the first multi-phase electric machine 5a and a common neutral point of the second multi-phase electric machine 5b for using at least one stator winding of each of the first multi-phase electric machine 5a and the second multi-phase electric machine 5b as a buck-boost inductance. Furthermore, the method comprises a fourth step S4: the bi-directional AC/DC converter is connected to the DC/DC converter and to the charging terminal 7 with or without passing through an intermediate electrical filter device. Finally, the method comprises a fifth step S5: an electronic control system 21 for controlling the operation of the vehicle electrical system is provided.

It is clear that the internal order of the above-described steps S1-S5 may be changed to include all possible combinations (i.e. a number of 5 | 120 combinations), considering that all steps are only concerned with providing various features and that no step depends on e.g. the calculation of another step.

According to another exemplary embodiment of the present disclosure, the method may include some additional steps described with reference to fig. 12. In particular, in addition to the above-described steps S1-S5, the method for charging the electrical storage system 6 may further comprise steps S6 and S7, the steps S6 and S7 involving details of the method for operating the vehicle electrical system in the vehicle charging mode of operation. The sixth method step S6 comprises: the DC/DC converter is provided with a first bidirectional switching device 30 configured for selectively opening and closing an electrical connection between a first connection point of the AC/DC converter and a common neutral point of the first multi-phase electric machine 5a, and with a second bidirectional switching device 31 configured for selectively opening and closing an electrical connection between the common neutral point of the first and second multi-phase

electric machines

5a, 5 b.

Furthermore, a seventh method step S7 comprises: each of the first and second

bi-directional switching devices

30 and 31 is controlled to have alternating on and off periods for achieving a voltage step-down during a vehicle charging mode of operation. During the first phase, when the first bi-directional switching device 30 is on and the second bi-directional switching device 31 is off, current flows from the first connection point of the AC/DC converter, via the first bi-directional switching device 30, the one or more stator windings of the first multi-phase electric machine 5a, the first inverter 9a, the second inverter 9b (via simultaneous bypass or non-bypass of the first few places to the electric storage system 6), the one or more stator windings of the second multi-phase electric machine 5b, and back to the second connection point of the AC/DC converter. Furthermore, during the second phase, when the first bi-directional switching device 30 is turned off and the second bi-directional switching device 31 is turned on, the charging current passes from the negative pole of the electrical storage system 6, via the second inverter 9b, the one or more stator windings of the second multi-phase electrical machine 5b, the second bi-directional switching device 31, the one or more stator windings of the first multi-phase electrical machine 5a, the first inverter 9a, and back to the positive terminal of the electrical storage system 6.

Obviously, as mentioned above, the internal order of the above steps S1-S6 may be changed to include all possible combinations, considering that the steps only involve providing various features, and that no step depends on, for example, the calculation result of another step. But the seventh step S7 must be at the end of the method.

According to another exemplary embodiment of the present disclosure, the method may comprise some additional steps described with reference to fig. 13. In particular, in addition to the above-described steps S1-S5, the method for charging the electrical storage system 6 may further comprise steps S6 and S7, steps S6 and S7 relating to details of the method for operating the vehicle electrical system in the vehicle-to-grid mode of operation. The sixth method step S6 comprises: the DC/DC converter is provided with a first bidirectional switching device 30 configured for selectively opening and closing an electrical connection between a first connection point of the AC/DC converter and a common neutral point of the first multi-phase electric machine 5a, and with a second bidirectional switching device 31 configured for selectively opening and closing an electrical connection between the common neutral point of the first and second multi-phase

electric machines

5a, 5 b.

Further, a seventh step S7 includes: each of the first and second

bi-directional switching devices

30, 31 is controlled to have alternating on and off periods for achieving voltage boost during the vehicle-to-grid mode of operation. During the first phase, when the first bi-directional switching device 30 is turned off and the second bi-directional switching device 31 is turned on, the discharge current flows from the positive pole of the electrical storage system 6, via the first inverter 9a, the one or more stator windings of the first multi-phase electrical machine 5a, the second bi-directional switching device 31, the one or more stator windings of the second multi-phase electrical machine 5b, the second inverter 9b, and back to the negative terminal of the electrical storage system 6. Furthermore, during the second phase, when the first bi-directional switching device 30 is on and the second bi-directional switching device 31 is off, the discharge current is from the second connection point of the AC/DC converter, via the one or more stator windings of the second multi-phase electric machine 5b, the second inverter 9b, the electric storage system 6, the first inverter 9a, the one or more stator windings of the first multi-phase electric machine 5a, the first bi-directional switching device 30, and back to the first connection point of the AC/DC converter.

Obviously, as mentioned above, the internal order of the steps S1-S6 described above may be varied to include all possible combinations, considering that the steps only relate to providing various features, and that no step depends on e.g. the calculation of another step. However, the seventh step S7 must be at the end of the method.

The term switch or electronic power switch refers herein to, for example, a power transistor or a semiconductor switch, such as a MOSFET, an IGBT, etc. The switches are provided in the first inverter 9a and the second inverter 9b for controlling the torque and/or speed of the first and second multiphase electric machines, and in the AC/DC converter 20 and the DC/DC converter 19 for controlling the charging voltage level.

It is to be understood that the above description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure as defined in the claims. In addition, modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular examples disclosed as the best mode contemplated for carrying out the teachings of the disclosure, but that the particular examples are illustrated by the accompanying drawings and described in the specification. Rather, the scope of the present disclosure is intended to include any embodiments falling within the foregoing description and the appended claims. Reference signs mentioned in the claims shall not be construed as limiting the scope of the claimed subject matter, their sole purpose being to make the claims easier to understand.

Claims

1. A vehicle electrical system comprising:

an electrical storage system (6);

-a first multiphase electric machine (5 a), the first multiphase electric machine (5 a) having a plurality of stator windings (8) connected to a common neutral point (29 a);

-a first inverter (9 a), the first inverter (9 a) being operatively connected to the electrical storage system (6) and the first multiphase electrical machine (5 a), wherein the first inverter (9 a) has a plurality of switch leads (10, 11, 12) with switches (10 a, 10b, 11a, 11b, 12a, 12 b);

-a second multiphase electric machine (5 b), the second multiphase electric machine (5 b) having a plurality of stator windings (13) connected to a common neutral point (29 b);

-a second inverter (9 b), the second inverter (9 b) being operatively connected to the electrical storage system (6) and the second multiphase electrical machine (5 b), wherein the second inverter (9 b) has a plurality of switch leads (14, 15, 16) with switches (14 a, 14 b);

a bi-directional buck-boost DC/DC converter operatively connected to the common neutral point (29 a) of the first multi-phase electric machine (5 a) and the common neutral point (29 b) of the second multi-phase electric machine (5 b) and configured for using at least one stator winding of each of the first multi-phase electric machine (5 a) and the second multi-phase electric machine (5 b) as a buck-boost inductance;

A bi-directional AC/DC converter operatively connected to the DC/DC converter and to a charging terminal (7) with or without intermediate electrical filter means; and

an electronic control system (21) for controlling the operation of the vehicle electrical system.

2. The vehicle electrical system of claim 1, wherein the electronic control system (21) is operably coupled to the bi-directional DC/DC converter and the first and second inverters (9 a, 9 b), and the electronic control system (21) is configured to:

-during a vehicle charging mode of operation, controlling operation of the DC/DC converter and first and/or second inverter for converting direct current supplied from the AC/DC converter into modified direct current and for supplying the modified direct current to the electrical storage system (6) via a common neutral point (29 a, 29 b) of the first and second multi-phase electrical machines (5 a, 5 b); and

-during a vehicle-to-grid mode of operation, controlling operation of the first and/or second inverter, and the DC/DC converter for supplying direct current from the electrical storage system (6) to the DC/DC converter via a common neutral point (29 a, 29 b) of the first and second multi-phase electrical machine (5 a, 5 b), and for converting the direct current into modified direct current for supply to the AC/DC converter.

3. The vehicle electrical system according to any one of the preceding claims, wherein the electronic control system (21) is operatively coupled with the bi-directional AC/DC converter and configured for:

-during a vehicle charging mode of operation, controlling operation of the AC/DC converter for converting single-phase alternating current or multi-phase alternating current received from a vehicle external charging power source (17) via the charging terminal (7) into direct current for supplying direct current to the DC/DC converter; and

-during a vehicle-to-grid mode of operation, controlling operation of the AC/DC converter for converting direct current received from the DC/DC converter into single-phase alternating current or multi-phase alternating current for supplying the alternating current to a vehicle external electrical load (18) via the charging terminal (7).

4. The vehicle electrical system of any one of the preceding claims, wherein the AC/DC converter has a grid side with two or three connection points for receiving and outputting single-phase or three-phase alternating current and a machine side with first and second connection points for receiving and outputting direct current;

And wherein the DC/DC converter comprises a first bi-directional switching device (30) and a second bi-directional switching device (31), the first bi-directional switching device (30) being configured for selectively opening and closing an electrical connection between a first connection point of the AC/DC converter and a common neutral point (29 a) of the first multi-phase electric machine (5 a), the second bi-directional switching device (31) being configured for selectively opening and closing an electrical connection between the common neutral points (29 a, 29 b) of the first multi-phase electric machine (5 a) and the second multi-phase electric machine (5 b).

5. The vehicle electrical system according to any one of the preceding claims, wherein during a vehicle charging mode of operation, the control system (21) is configured for operating the DC/DC converter with alternating on and off periods when voltage step-down control is performed on each of the first bi-directional switching device (30) and the second bi-directional switching device (31);

so that during a first phase, when the first bi-directional switching device (30) is on and the second bi-directional switching device (31) is off, current can flow from the first connection point of the AC/DC converter, via the first bi-directional switching device (30), one or more stator windings of the first multi-phase electric machine (5 a), the first inverter (9 a), the second inverter (9 b), while bypassing or not bypassing the electric storage system (6), and back to the second connection point of the AC/DC converter via one or more stator windings of the second multi-phase electric machine (5 b); and

So that during a second phase, when the first bi-directional switching device (30) is off and the second bi-directional switching device (31) is on, charging current can flow from the negative pole of the electrical storage system (6), via the second inverter (9 b), one or more stator windings of the second multi-phase electrical machine (5 b), the second bi-directional switching device (31), one or more stator windings of the first multi-phase electrical machine (5 a), the first inverter (9 a), and back to the positive terminal of the electrical storage system (6).

6. The vehicle electrical system according to any one of the preceding claims, wherein during a vehicle charging mode of operation, the control system (21) is configured to operate the first bidirectional switching device (30) with a first set of alternating on and off periods and to operate the second bidirectional switching device (31) with a second set of alternating on and off periods, which are set substantially synchronous and inverted with the first set of alternating on and off periods.

7. The vehicle electrical system according to any one of the preceding claims, wherein each of the first inverter (9 a) and the second inverter (9 b) comprises at least one inverter leg for each phase of the associated multi-phase electric machine, and wherein each inverter leg comprises an upper switch associated with a positive dc bus, the upper switch and a lower switch associated with a negative dc bus being connected in series, wherein the control system (21) is configured for, during the vehicle charging mode of operation,

Setting all upper and lower switches of the first inverter (9 a) and the second inverter (9 b) to an open state during both the first phase and the second phase; or alternatively

Setting all upper and lower switches of the first inverter (9 a) and all lower switches of the second inverter (9 b) to an open state during both the first phase and the second phase, setting one, two, three or more upper switches of the second inverter (9 b) to a closed state during the first phase, and setting all upper switches of the second inverter (9 b) to an open state during the second phase; or alternatively

-setting all upper and lower switches of the second inverter (9 b) and all upper switches of the first inverter (9 a) to an open state during both the first phase and the second phase, -setting one, two, three or more lower switches of the first inverter (9 a) to a closed state during the first phase, and-setting all lower switches of the first inverter (9 a) to an open state during the second phase.

8. The vehicle electrical system according to any of the preceding claims, wherein an electrical connection extending from a common neutral point (29 a) of the first multi-phase electrical machine (5 a) to a common neutral point (29 b) of the second multi-phase electrical machine (5 b) via the second bi-directional switching device (31) is devoid of any substantial inductor.

9. The vehicle electrical system according to any one of the preceding claims, wherein the vehicle electrical system is free of a DC/DC converter in an electrical power supply path extending between the electrical storage system (6) and any one of the first inverter (9 a) and the second inverter (9 b).

10. The vehicle electrical system according to any one of the preceding claims, wherein the AC/DC converter is a single-phase or three-phase active front-end rectifier comprising a plurality of switch legs connected between a positive bus and a negative bus of a direct current link, wherein each switch leg has at least two switches connected in series by an intermediate conductor, wherein a grid side of the AC/DC converter comprises two or three connection points electrically connected to the charging terminal (7) for receiving single-phase or three-phase alternating current from a vehicle external charging source (17) or a vehicle external electrical load (18) or outputting single-phase or three-phase alternating current to a vehicle external charging source (17) or a vehicle external electrical load (18), wherein each of the two or three connection points is electrically connected to a separate intermediate conductor of the plurality of switch legs.

11. The vehicle electrical system according to any one of the preceding claims, wherein during a vehicle-to-grid operation mode, the control system (21) is configured for operating the DC/DC converter with alternating on and off periods when voltage boosting each of the first bi-directional switching device (30) and the second bi-directional switching device (31),

so that during a first phase, when the first bi-directional switching device (30) is off and the second bi-directional switching device (31) is on, current can be returned from the positive pole of the electrical storage system (6) via the first inverter (9 a), one or more stator windings of the first multi-phase electrical machine (5 a), the second bi-directional switching device (31), one or more stator windings of the second multi-phase electrical machine (5 b), the second inverter (9 b), back to the negative terminal of the electrical storage system (6); and

so that during a second phase, when the first bi-directional switching device (30) is on and the second bi-directional switching device (31) is off, current can be returned from the second connection point of the AC/DC converter via one or more stator windings of the second multi-phase electric machine (5 b), the second inverter (9 b), the electrical storage system (6), the first inverter (9 a), one or more stator windings of the first multi-phase electric machine (5 a), the first bi-directional switching device (30) back to the first connection point of the AC/DC converter.

12. The vehicle electrical system according to any one of the preceding claims, wherein each of the first inverter (9 a) and the second inverter (9 b) comprises at least one inverter leg for each phase of an associated multiphase electrical machine, and wherein each inverter leg comprises an upper switch associated with a positive dc bus, the upper switch and a lower switch associated with a negative dc bus being connected in series;

wherein the control system (21) is configured for setting one, two, three or more upper switches of the first inverter (9 a) to a closed state during both the first phase and the second phase, setting one, two, three or more lower switches of the second inverter (9 b) to a closed state during both the first phase and the second phase, and setting all lower switches of the first inverter (9 a) and all upper switches of the second inverter (9 b) to an open state during both the first phase and the second phase, during the vehicle-to-grid operation mode.

13. The vehicle electrical system according to any one of the preceding claims, wherein the control system (21) is configured for controlling the first inverter and/or the second inverter based on an angular position of a rotor of the first multi-phase electric machine (5 a) and/or the second multi-phase electric machine (5 b) during a vehicle-to-grid or vehicle charging mode of operation.

14. The vehicle electrical system according to any one of the preceding claims, wherein the control system (21) is configured for:

during a vehicle-to-grid mode of operation, selecting which of the one or more upper switches of the first inverter (9 a) and which of the one or more lower switches of the second inverter (9 b) should be set to a closed state during the first and second phases based on an angular position of a rotor of the first and/or second multi-phase electric machine (5 a, 5 b); and/or

During a vehicle charging mode of operation, based on an angular position of a rotor of the first multi-phase electric machine (5 a) and/or the second multi-phase electric machine (5 b), it is selected which of the one or more upper switches of the second inverter (9 b) should be set to a closed state during the first phase, or which of the one or more lower switches of the first inverter (9 a) should be set to a closed state during the first phase.

15. A method for charging an electrical storage system (6) of a vehicle electrical system, the method comprising:

-connecting a first inverter (9 a) to the electrical storage system (6) and to a first multiphase electrical machine (5 a), the first multiphase electrical machine (5 a) having a plurality of stator windings (8) connected to a common neutral point (29 a), wherein the first inverter (9 a) has a plurality of switch leads (10, 11, 12) with switches (10 a, 10b, 11a, 11b, 12a, 12 b);

-connecting a second inverter (9 b) to the electrical storage system (6) and a second multiphase electrical machine (5 b) having a plurality of stator windings (13) connected to a common neutral point (29 b), wherein the second inverter (9 b) has a plurality of switch leads (14, 15, 16) with switches (14 a, 14 b);

connecting a bi-directional buck-boost DC/DC converter to a common neutral point (29 a) of the first multi-phase electric machine (5 a) and to a common neutral point (29 b) of the second multi-phase electric machine (5 b) for using at least one stator winding of each of the first multi-phase electric machine (5 a) and the second multi-phase electric machine (5 b) as a buck-boost inductance;

-connecting a bi-directional AC/DC converter with or without intermediate electrical filter means to said DC/DC converter and to a charging terminal (7); and

an electronic control system (21) for controlling operation of the vehicle electrical system is provided.